Can opera singers shatter glass with their high notes?

May 11, 1990

Dear Cecil:

Can operatic sopranos really break glasses with their high notes? What note does the trick? How come they don't break windows and eyeglasses and whatnot at the same time? Can women do this better than men? Can I learn how? Or have I been the victim of an elaborate hoax?

— Vox Clamantis, Chicago

Cecil replies:

I dunno — you ever buy whole-life insurance? Now there was a hoax. Shattering glasses, on the other hand, is entirely legit. Enrico Caruso and Italian opera singer Beniamino Gigli are said to have managed it, and I seem to remember Ella Fitzgerald doing it once in a Memorex commercial.

The technique is simple. First you find somebody with perfect pitch and leather lungs. Then get a crystal glass and tap it with a spoon to determine its natural frequency of vibration (this varies with the glass). Next have the singer let loose with precisely the same note. When he or she is dead-on pitchwise, the glass will commence to resonate, i.e., vibrate. Then turn up the V. Bingo, instant ground glass.

What we have here is a graphic demonstration of forced oscillation resonance. If something has a natural rate of vibration, pump in more energy of the same rate and with luck the thing will vibrate so bad it'll self-destruct. It's like giving somebody on a swing a good shove at the top of every arc — soon they'll reach escape velocity and soon after that they'll be picking vertebrae out of their sinuses.

Breaking glasses, however, is strictly light entertainment. For real forced oscillation action you want a suspension bridge. In 1831 troops crossing a suspension bridge near Manchester, England, supposedly marched in time to the bridge's sway. Boy, did they get a surprise. Ever since soldiers have been told to break step when crossing bridges. The same fate befell the Tacoma Narrows suspension bridge in Washington State on November 7, 1940, only it wasn't soldiers that caused it to collapse, it was the wind.

But back to the home front. Crystal is more vulnerable than ordinary glass because it has more internal structure, which allows waves to propagate. (Take my word for it.) But you can annihilate damn near anything given enough volume. One physicist, obviously one of your classic Roommates From Hell, claims he inadvertently shattered a glass lamp shade while playing the clarinet.

Think of the possibilities. Most of us don't have the pipes to break glasses by sheer voice power, but we all have clarinets, don't we? Unfortunately, none of the standard physics cookbooks gives a detailed glass-bustin' recipe. Too bad. A fascinating classroom demonstration like this would surely convince many young people to give up MTV and devote their lives to science.

Shattering myths

Dear Cecil:

In the matter of glass-shattering vocalism, Cecil seems to have been led astray by Gunter Grass's fictional tin drummer, Oskar. In fact, there is no authentic record of glass being broken by the unamplified human voice. Dorothy Caruso categorically denied rumors that her late husband had accomplished the feat; a fortiori it was beyond Gigli's comparatively feeble instrument. Practically speaking, there are reasons to believe the thing impossible, and without going into technical detail, the following are among them: (1) Glass is simply much too strong. Try shattering a wine glass in your (gloved) fingers. Not easy. Now imagine doing the same with the puny little bands of your vocal cords. (2) Coupling acoustic energy from larynx-to-air-to-glass is highly inefficient due to large impedance mismatches; by contrast, marching troops couple very efficiently to bridge platforms. (3) In glass shattering attempts, resonance or no resonance, the glass structure finds other ways to dissipate energy short of fracturing. Remember the playground swing in which successive small but well-timed swings sent your sister sailing higher and higher? And the tales of going "over the top" when the process went critical? Alas! it never happened, because other dynamic processes supervened ("Gee, Mom, we were just playing") before the longed-for loop could occur.

— Timon, Dallas

Cecil replies:

A fortiori? Supervened? Boy, I see I wasn't the only one to get a Word-A-Day calendar for Christmas. As for glasses, let's clarify one thing: it is certainly possible to shatter glasses with the amplified human voice. The folks at the Memtek company in Fort Worth, Texas, which makes Memorex recording tape, do it all the time for sales demonstrations and whatnot. (You'll remember that Memorex used to run those TV commercials showing Ella Fitzgerald and others breaking glasses with their voices.)

What's more, they do it pretty much the way I described: they go out and get a drinking glass with high lead content, tunk it with a rubber mallet to make it ring, then read the frequency on an analyzer. Then they get a singer to sing the same note (typically F above middle C), amplify it to maybe 92, 94 decibels, and with luck you get glass shrapnellini. Memorex technicians using a strobe have found that prior to the break the sound causes the rim of the glass to deflect as much as a quarter inch. (I get this from Rick Needham, engineering manager, lest you think I am making this up.)

Your beef is that I suggested this could be done with the unamplified human voice. I'll grant I haven't been able to turn up a documented instance of this, but it seems subsidiary to my main point, which is that you can shatter glasses with sound, and furthermore that the human voice, which can generate a relatively pure tone, is well suited to this purpose. Furthermore, none of the technical people I spoke to about this seemed to think doing it by voice alone was completely impossible. Admittedly 90-plus decibels is pretty damn loud, but one of the reasons the Memtek folks crank it up that much is that they're using an inexpensive ($7) glass rather than fine crystal, which is more fragile. So let's not be so negative, Timsy. It's the can-do attitude that has made this country great.

Bridge crash news flash!

In his recent treatise on whether singers can break glasses with their voices, Cecil mentioned "forced oscillation resonance," in which an external force amplifies the natural vibration of an object, sometimes with destructive results. As an example he cited the 1940 collapse of the Tacoma Narrows bridge. The usual explanation for this disaster is that the wind gusted (to be precise, "generated a train of vortices") in perfect synch with the bridge's natural rate of bounce, causing its demise.

Reader Wilbur Pan has alerted us to a recent report in Science News heaping abuse on this widely held view. Mathematicians Joseph McKenna and Alan Lazer doubt that a storm could produce the perfectly timed winds required. They're working on a "non-linear" model of bridge behavior they hope will provide a better explanation. The main problem apparently is that when the roadway of a lightly constructed suspension bridge flexes, the cables supporting it go slack, introducing an element of unpredictability in which little causes (i.e., the wind) produce big results (i.e., a collapsing bridge). They hope to have the mathematical model describing this effect finished in five years — not the most aggressive schedule in the world, but apparently this is government work. You'll read about it here first.